1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and method for handling tubulars and drilling with tubulars to form a wellbore. More particularly, embodiments of the present invention relate to drilling with casing. Even more particularly, embodiments of the present invention relate to a gripping apparatus for supporting casing for use in a drilling with casing operation.
2. Description of the Related Art
In conventional well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. In drilling operations, a drilling rig is disposed above the subterranean formation where the access will be formed. A rig floor of the drilling rig is the surface from which casing strings, cutting structures, and other supplies are lowered to form a subterranean wellbore lined with casing. A hole is formed in a portion of the rig floor above the desired location of the wellbore. The axis that runs through the center of the hole formed in the rig floor is well center.
Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on the drilling rig. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore.
Often, it is necessary to conduct a pipe handling operation to connect sections of casing to form a casing string or to connect sections of tubular to form a tubular string. The pipe handling operation to connect sections of casing may be used to produce a casing string which extends to the drilled depth. Pipe handling operations require the connection of casing sections to one another to line the wellbore with casing. To threadedly connect the casing strings, each casing section may be retrieved from its original location (e.g., a rack beside the drilling platform) and suspended above well center so that each casing section is in line with the casing section previously disposed within the wellbore. The threaded connection is made up by a device which imparts torque to one casing section relative to the other, such as a power tong or a top drive. The casing string formed of the two casing sections is then lowered into the previously drilled wellbore.
It is common to employ more than one string of casing in a wellbore. In this respect, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is removed. Sections of casing are connected to one another and lowered into the wellbore using the pipe handling operation described above to form a first string of casing longitudinally fixed in the drilled out portion of the wellbore. Next, the well is drilled to a second designated depth through the first casing string, and a second, smaller diameter string of casing comprising casing sections is hung off of the first string of casing. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wellbores are typically formed with two or more strings of casing.
The handling of casing strings has traditionally been performed with the aid of a spider along with an elevator. Spiders and elevators are used to grip the casing strings at various stages of a pipe handling operation. Typically, spiders include a plurality of slips circumferentially surrounding the exterior of the casing string. The slips are housed in what is commonly referred to as a “bowl”. The bowl is regarded to be the surfaces on the inner bore of the spider. The inner sides of the slips usually carry teeth formed on hard metal dies for engaging the pipe string. The exterior surface of the slips and the interior surface of the bowl have opposing engaging surfaces which are inclined and downwardly converging. The inclined surfaces allow the slip to move vertically and radially relative to the bowl. In effect, the inclined surfaces serve as a camming surface for engaging the slip with the casing string. Thus, when the weight of the casing string is transferred to the slips, the slips will move downwardly with respect to the bowl. As the slips move downward along the inclined surfaces, the inclined surfaces urge the slips to move radially inward to engage the casing string. In this respect, this feature of the spider is referred to as “self tightening.” Further, the slips are designed to prohibit release of the casing string until the casing string load is supported by another means such as the elevator.
In the making up or breaking out of casing string and/or tubular string connections, the spider is typically used for securing the casing string or tubular string in the wellbore. Additionally, an elevator suspended from a rig hook is used in tandem with the spider. The elevator may include a self-tightening feature similar to the one in the spider. In operation, the spider remains stationary while securing the casing string in the wellbore. The elevator positions a casing string section above the casing string for connection. After completing the connection, the elevator pulls up on the casing string to release the casing string from the slips of the spider. Freed from the spider, the elevator may now lower the casing string into the wellbore. Before the casing string is released from the elevator, the spider is allowed to engage the pipe string again to support the casing string. After the load of the casing string is switched back to the spider, the elevator may release the casing string and continue the makeup process.
As an alternative to the conventional method, drilling with casing is a method often used to place casing strings within the wellbore. This method involves attaching a cutting structure in the form of a drill bit to the lower end of the same string of casing which will line the wellbore. Drilling with casing is often the preferred method of well completion because only one run-in of the working string into the wellbore is necessary to form and line the wellbore for each casing string.
Drilling with casing is typically accomplished using a top drive powered by a motor because the top drive is capable of performing both functions of imparting torque to the casing string to make up the connection between casing strings during pipe handling operations and drilling the casing string into the formation. FIG. 1 shows two exemplary gripping apparatuses 100, 200 used in a typical drilling with casing operation. Connected to a drilling rig 105 is a traveling block 115 suspended by wires 150 from draw works 120. A top drive 110 with an elevator 200 connected thereto is suspended from the traveling block 115. The elevator 200 typically is connected to the top drive 110 by bails 125. A motor 140 is the part of the top drive 110 used to rotate a first and second casing string 210, 130 when drilling with casing or to rotate the second casing string 130 when connecting the second casing string 130 to the first casing string 210 which has been previously located within a wellbore 180. Located within a rig floor 135 of the drilling rig 105 is a rotary table 145 into which the spider 100 can be placed. The spider 100 and the elevator 200 are both used to grippingly and rotationally support casing strings 210, 130 axially at various stages of a typical operation; therefore, both the spider 100 and the elevator 200 are deemed “gripping apparatuses” for purposes of the present invention.
Current spiders and elevators useable in drilling with casing operations are capable of either being actuated to grippingly engage the casing string to prevent rotational or axial movement of the casing string or, in the alternative, of being unactuated to release the casing string completely to allow axial and rotational movement of the casing string while the casing string is drilled into the formation. Because only these two positions are possible with current gripping apparatuses, problems occur when using the gripping apparatuses while drilling with casing. When performing a drilling with casing operation with the current spiders or elevators in the unactuated position, the casing string is not centered within the wellbore while drilling because the casing string is not supported along its diameter and thus is free to move within the wellbore while drilling. Furthermore, because the casing string is loose inside the gripping apparatus, the slips of the gripping apparatus often contact the outer diameter of the casing string being rotated while drilling and can cause damage to the casing string. When the slips contact the outer diameter of the casing string, damage may also result to the slips. Additionally, the rotational movement is hindered in the current gripping apparatus by any contact of the casing string with parts of the gripping apparatus.
There is therefore a need for a gripping apparatus useful during a drilling with casing operation. There is a further need for a gripping apparatus which is capable of accommodating more than one pipe size so that the casing is centered on the well center while drilling with casing. There is an even further need for a gripping apparatus which allows the casing string to freely rotate while preventing damage to the casing and positioning the casing over the well center during a drilling with casing operation.